JPH0296414A - Surface acoustic wave device, its manufacture, communication equipment using it and method for adjusting the equipment - Google Patents

Abstract

PURPOSE:To miniaturize the satisfactory equipment of a shoulder characteristic as a filter and to reduce the influence of the diffraction effect by providing the reflector of the surface acoustic wave at least at one side of an interdigital electrode. CONSTITUTION:An output interdigital electrode 2 and an input interdigital electrode 3 on a surface acoustic wave substrate 1 are arranged, a sound absorbing agent 4 to suppress the reflection from a substrate edge surface is applied to the edge of the substrate 1 and a short strip type reflector 5 is arranged at both sides of the electrode 3. The impulse to occur from the electrode 3 is closed at the section of the reflector 5, a part of it successively passes through the reflector 5 and arrives at an electrode 2. Consequently, for an impulse response train (broken line 7), the length of the response time is longer than an impulse response train (real line 6) before the reflector 5 is provided and equal to the condition in which the interdigital electrode equivalent to the length of the response time is provided. Since the number of the electrodes of the interdigital electrode is not increased and it is not necessary to make small the aperture, the device, which is small, has a small quantity of the influence of the diffraction effect, and is satisfactory in the shoulder characteristic, can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a surface acoustic wave device that has good shoulder characteristics and out-of-band characteristics in a frequency band when used as a filter, and a method for manufacturing and adjusting the same.

[Conventional OJ technology]

Conventionally, as a means to improve the shoulder characteristics (steepness of the attenuation characteristics at the edge of the filter band) of surface acoustic wave filters, for example,
IEE Transactions on Microwave Theory and Techniques, MTT21 (IEEE, TRANS, ON
MICROWAVE THEORY AND TEC
) I-NIQUES, VOL.

MTT-21) i4 issue, April 1975, 206-2
Multi-string coupler described on page 15
There are technologies such as

[Problem to be solved by the invention]

In the above conventional technology, in order to improve the shoulder characteristics, the number of interdigital electrodes must be increased, resulting in a larger chip shape and an unavoidable increase in cost.As for the relationship between the zero-chip characteristics and the number of electrodes, For example, IEE Transaction O/Microwave Theory and Techniques 21 (IEEE
, TRANS, ONMICRO-WAVE THEOR
Y ANDTECHNIQUES, VOL, MTT
-21M! No. 4, April 1973, No. 162-1
This is discussed on page 75.

Furthermore, in order to improve the shoulder characteristics, the number of electrode pairs must be increased in the conventional technology as described above, which increases the radiation conductance of the interdigital electrodes and the reflection (RW) determined by the conditions with the electrical load. ) increases. Therefore, usually
In order to suppress the above-mentioned reflection, the aperture of the interdigital electrode must be narrowed, and in that case, the influence of the diffraction effect of surface acoustic waves increases, resulting in deterioration of the filter characteristics such as side lobes. .

The present invention aims to reduce the size of a surface acoustic wave device having good shoulder characteristics as a filter and to reduce the shadow 9 of the diffraction effect.

[Means to solve the problem]

In order to achieve the above object, in the present invention, at least one piece of the interdigital electrode (14 sigma wave σ) reflectors are provided in the surface acoustic wave device.

[Effect]

By providing a reflector next to the interdigital electrode, the surface acoustic wave emitted from the interdigital electrode is reflected by the reflector lζ, which is equivalent to an apparent increase in the number of wJ oscillation sources of the surface acoustic wave. The shoulder characteristics can be improved without increasing the chip size. Furthermore, in order to improve the shoulder characteristics without increasing the number of pairs of interdigital electrodes, it is not necessary to make the aperture of the BL pole small (and the shadow of the diffraction effect can be suppressed).

〔Example〕

A first embodiment of the present invention will be described using FIGS. 1 to 3. FIG. 1 is a plan view showing the first embodiment 8 in a wedge-like manner. An output interdigital electrode 2 and an input interdigital electrode 3 are arranged on a surface acoustic wave substrate 1, and a sound absorbing material 4 is applied to the edge of the substrate to suppress reflection from the end surface of the substrate. In addition, short strip reflectors 5 are placed on both sides of the input interdigital electrode.
is installed. The input and output interdigital electrodes were of the split-connect type. Next, the principle of operation of this embodiment will be explained with reference to FIG. In FIG. 2, the horizontal axis represents time and the vertical axis represents the intensity K (amplitude) of the surface acoustic wave excitation source, and schematically shows an impulse response viewed from a position away from the interdigital electrode.

The response shown by the solid line 6 is for the input T-shaped electrode alone (therefore, no reflector is installed), and the response shown by the broken line 7 is the response after the reflector 5 is installed. The impulses generated from the interdigital transducers are confined between the reflectors 5, and a portion of them sequentially passes through the reflectors 58 and reaches the output interdigital electrodes 2. Therefore, as shown in diagram M2, the impulse response train (dashed line 7) has a longer response time than the impulse response train (solid line 6) before the reflector is installed, and corresponds to the length of the above response time. This is equivalent to the state in which interdigital electrodes are arranged.Since there is no need to increase the number of interdigital electrodes and there is no need to make the aperture smaller, it is small and has good shoulder characteristics with less influence of diffraction effects. A surface acoustic wave device is obtained. FIG. 3 shows the frequency characteristics of the attenuation amount of the IF filter of a domestic television receiver. The broken line 8 is the characteristic of a normal IF filter, and the dashed line 10 is the characteristic of a conventional IF filter in which the number of electrode pairs is increased, the shoulder characteristic of the chroma tilt part is improved, and the aperture is narrowed to reduce reflection by RW. The number of pairs of excitation sources (impulses) of the weighted interdigital electrode on the input side is 150 pairs, the lower opening is 50 μm, and the number of pairs of excitation sources (impulses) of the weighted interdigital electrode on the output side is 15 pairs, and the opening of the regular type electrode is 15 pairs. ff1LiT
An AOS board is used. In the conventional configuration described above, as shown in the figure, the zero solid line 9 in which deterioration of the side lobe characteristics and trap (attenuation pole) characteristics was observed indicates the characteristics of the filter according to the present invention ζ. The number of excitation source pairs of the input interdigital electrode 5 is 60, and the number of electrodes of the reflector 5 is 20.
Therefore, the length of the electrode on the input side including the reflector is approximately 8
The number of pairs is 0, which is about half the value of 150 pairs in the conventional filter mentioned above. The number of pairs and apertures of the output normal interdigital electrodes are the same as in the conventional case. The overall length of the chip is approximately 374mm compared to the conventional one, achieving a smaller size.In addition, since the aperture of the input interdigital pole is not narrowed, diffraction effects are suppressed and good out-of-band characteristics are achieved. It is being

Looking at the characteristics indicated by the solid line in FIG. 3, the shoulder characteristics and out-of-band characteristics are good, but ripples are seen within the band. This is due to the effect of reflection by the reflector 5.

Next, a second embodiment in which the above-mentioned reflection is suppressed will be explained with reference to FIGS. 4 and 5. FIG. , an equivalent circuit diagram is shown below). Here, S is the element of the scattering matrix of the interdigital electrode and reflector (input port 81.
output port 82), T,, T, is the transmission coefficient between the reflector 5 and the interdigital electrode 3, 0, where the subscript a is the previous reflector, and the subscript a is the interdigital! pole, subscript C
The calculation result is as follows.

Also, for reference, the transmission coefficient T is shown below. Now considering the vicinity of the center frequency of the filter, the condition for the reflected waves to cancel each other out is T, ='p2=6±J-j=± j
−(3), and consider each scattering matrix as a real number (because it is near the center frequency, the phase term of each term is all TI + '
rt), each reflection b, T
Reversibility and symmetry of the n-shaped electrode (S+t = St+,
So = Su) ') Considering that the front and rear reflectors have the same structure, S〒1 = crystal = r, C4) Sk2 = Srt = t a (5) So
= rb (6) S1*= t b
(7) becomes. Now, since the loss in the reflector and the interdigital electrode is sufficiently small, from the law of conservation of energy, ta + r, = 1 (9
)tb + rb = 1 - (1o) holds, so equation (8) becomes. Since r=o in the absence of reflection, rH(4
r knee 2ra)+rb(3r;-1)+2ra-2ra
=O(By solving the quadratic equation (12), the relationship is obtained. That is, the reflection coefficients of the interdigital electrodes and the reflector are determined so as to satisfy Equation (13) 8, and the electrode at the end of the reflector is The distance between the center of
Reflected waves can be suppressed by setting TI=T1=e±JT.

Next, a second embodiment will be described in which the present invention is applied to an IF filter for a domestic television receiver. The input interdigital electrode was a regular solid type electrode, and λ/4 solid type short strip type reflectors were arranged on both sides thereof. The number of excitation source pairs of the regular type electrode was 15 (31 electrodes), and the number of reflectors was 16.The interdigital electrode on the 0 output side had an aperture weighted split-connect type structure, and the number of excitation source pairs was 60.
．． There were 5 pairs.

r, = 0.108, rl, = 0.054, (
15) formula is almost satisfied. The distance between the electrode and the reflector was 3/4λ (the distance between the centers of the respective end electrodes). FIG. 5 shows the frequency characteristics of the attenuation amount in the second embodiment. The reflection characteristics within the C band, where the solid line 11 indicates attenuation it, are improved,
The ripple is small.0 Thus, in the second example, a small filter with small ripple near the center frequency and good shoulder characteristics was obtained.

In Example @2, by specifying the reflection coefficient of the reflector, it was possible to improve the ripple characteristics near the center frequency, but as can be seen from Figure 5, the reflected wave The degree of suppression is decreasing and the ripple is increasing. This is because the center position of the reflector and the interdigital electrode are far apart, so the phase rotation of T, , T is fast, and it is not possible to keep T1゜T-e±J-i constant as mentioned above. This is because reflection increases rapidly when the frequency deviates from the center frequency.

The fifth embodiment improves the above-mentioned drawbacks. Equation (15) is r
If a+rb is sufficiently small relative to 1, then rb'%2r
a (1'). Further, the MEL (reflection determined by the geometric shape l of the electrode) of the solid type short strip reflector and the solid type interdigital electrode is expressed by the following equation.

Here, Zr is the ratio of the propagation impedance of surface acoustic waves in a place with an electrode and a place without an electrode, and N is the number of electrodes. Generally, Zr is sufficiently close to 1ζ, so zr=1+e(ε<1
) −(16). Equation (15) is expressed as. When l/'I is smaller than 1 in terms of light (N is small), jr l ''qNt (1
8). Applying the result of (18) to the above-mentioned reflector (indicated by subscript a) and interdigital electrode (indicated by subscript sum) and using equation (14), Nbg 'q 2 Nm' Nb-2Na (19 ) relationship is obtained. That is, if the number of electrodes is small enough,
Ratio of the number of electrodes of the reflector to the number of electrodes of the interdigital electrode: 81:
If you set it to 2, you can create ink that suppresses the overall reflection. For example, suppressing the reflection of a pair of interdigital electrodes of a pair of excitation sources can be achieved by arranging a reflector consisting of one electrode at a distance of 1 λ 10 λ (n is a natural number) on both sides. n=
If it is set to 1, it is possible to sufficiently suppress the wide-band electrostatic reflection wave.

A desired frequency characteristic is obtained by arranging a plurality of electrode groups (1 pair of excitation source pairs of interdigital electrodes and 1 reflector electrode (1 set)) in the surface wave propagation direction.

In the NX6 diagram, a portion 13 surrounded by a zero-dashed line showing the configuration is the basic configuration. The split-type electrodes d installed between the basic components are used to make the reflector part a short strip type (remove the RW portion of the reflector part). The reason for using the sugerite type is to suppress the MEL component there. Therefore, the interdigital electrode 12 has a structure in which a reflector is disposed inside.

@5 As an example, a case will be described in which a surface acoustic wave device having the input interdigital electrode 8 having the above structure is applied to an IF filter of a domestic television receiver. Basic structure: 85 interdigitated electrodes connected to each other were used as the input regular interdigital electrodes, and the output interdigital electrodes were of the aperture weighted split-connect type.

The aperture of the input normal type electrode was 1500 μm, the number of excitation source pairs of the output interdigital electrode was 120, and the aperture was 1000 μm. The solid line 14 in Figure 7 shows the wave number characteristics of this filter.
Indicated by Since the reflected waves are suppressed in a wide band, ripples are reduced.0 As described above, if the third embodiment is used, a small surface acoustic wave filter with good shoulder characteristics and suppressed ripples in a wide band can be obtained. The fourth embodiment will be explained with reference to FIGS. 8, w, and 9. Figure @8 schematically shows the fourth embodiment, in which both *lr of the input (output) T-shaped electrode 15 opposite to the output (input) T-shaped electrode 2 are provided with the same structure as in each of the above embodiments. , a reflector 5 is provided. When the reflectors are arranged in this way, energy is trapped between the reflectors and the shoulder characteristics can be improved, but at the same time, the Q increases at the band edge frequency, so there is no group at that frequency. This results in an increase in delay time. If flatness of the group delay time is essential, the group delay time characteristic of the interdigital electrode 15 must be made phase-leading in advance. The broken line 16 indicates the characteristics before the reflector is installed, and the actual fM17 is the characteristic after casting. According to the fourth embodiment, a small, high-performance filter with a steep shoulder characteristic and a constant group delay can be obtained.

Next, a fifth embodiment will be explained with reference to FIGS. 10 and 11. As can be seen from FIG. 9, in the fourth embodiment, it is not possible to completely keep # slow grinding constant, and ripples occur within the band. This is because the reflector consists of a large number of electrodes, so energy is trapped within the reflector, and the overall impulse response does not have symmetrical characteristics on the time axis. Therefore, if flatness of the group delay time is essential, a completely reflective surface is required.

FIG. 10 schematically shows the fifth embodiment, in which the input (output) interdigital shape 4 is opposed to the output (input) interdigital shape 'wL pole 2.
A split-connect interdigital electrode reflector with an α5 excitation source is disposed at one end of the pole 18, and the capacitance t of the electrode is canceled out using an inductance 20 in order to obtain a high reflection coefficient. As described above, since the interdigital electrode type reflector can obtain a high reflection coefficient even with a small logarithm, it is effective for ensuring the flatness 8 of the group delay. Alternatively, it is possible to use the end face of the substrate as a means for obtaining the perfect reflective surface 8, but it is thought that the above method is more effective due to problems such as substrate processing accuracy and chipping. In FIG. 11, the group delay time characteristic of the @5 embodiment is shown by a solid line 21. It can be seen that the flatness within the band is improved compared to the fourth example.

As described above, using the fifth embodiment allows the group delay characteristics to be further improved.

Next, a sixth embodiment will be described using FIG. The above-mentioned reflector is intended to improve the shoulder characteristic at the edge of the filter band, but if the reflection coefficient of the reflector is too large or too small, the flatness of the in-band characteristic of the amount of attenuation deteriorates. Furthermore, if the reflected wave phase of the reflector deviates from the optimum value, Q values other than the desired frequency will increase, resulting in deterioration of shoulder characteristics and deterioration of in-band flatness of the amount of attenuation. FIG. 12 shows a method for adjusting the reflection coefficient of the reflector in such a case. That is, a purulent-retaining film such as a resist film is formed only on the necessary portions of the reflector 5 (the portions to be left) and etching is performed to remove the unnecessary portions 22.
8. Trimming is performed sequentially starting from the edge force) to adjust the reflection coefficient. 1. By using this example, it is possible to improve the deterioration of the frequency characteristics due to the deviation of the reflection characteristics, which is effective in improving the yield. The seventh embodiment relates to a method for adjusting the phase of the reflected wave of a reflector. FIG. 13 shows a method for adjusting the reflector of the seventh embodiment. The reflector 5 is made of a short strip electrode. Sequentially, open strip portions are formed at the cut points e using a trimming technique such as a laser cutter, an ultrasonic cutter, etc., and the phase of the reflected waves is adjusted.Using this embodiment has the effect of improving the yield.

The implementation @88 relates to a method for adjusting the frequency characteristics of a communication device using the surface acoustic wave device of the present invention equipped with an interdigital electrode reflector in its circuit. FIG. 14 schematically shows the eighth embodiment. A transducer-shaped electrode reflector 19 is disposed next to the input (output) transducer-shaped electrode 18 that faces the output (input) transducer-shaped electrode 2 . A variable inductance 238 is arranged in the external circuit of the surface acoustic wave device and electrically connected to the interdigital electrode type reflector 19. The reflection characteristics of the interdigital electrode can be adjusted by increasing the matching inductance value +i. Therefore, after installing the elastic surface fft of the present invention in a communication device, the above variable inductance value is adjusted to 8FA. If this embodiment is used, it is effective that the frequency characteristics 8 can be adjusted while being mounted on a communication device.

A description will be given of an embodiment in which the present invention is applied to Tsushin@i. FIG. 15 is a block diagram of a television receiver according to a ninth embodiment. IF specific output of the tuner 24 Connected to the elastic surface arytenoid riL 25 of the present invention, the surface acoustic wave device 25
The output is divided into two systems, one system is the video detection circuit 261
The other system is input to the audio detection circuit 271. The characteristics of the surface acoustic wave device 25 of this embodiment are as follows.
With the characteristics shown in the figure, the screen resolution is improved by increasing the chroma level, and the technology of the present invention is used to attenuate the audio level, so cross color 920
Good characteristics are obtained without interference such as Kh beat.

Next, the tenth embodiment 1 will be explained with reference to FIGS. 16 and 17. Figure 16 shows the satellite number transmission and reception II of the 10th embodiment.
FIG. The signal down-converted by the outdoor unit 28 is sent to the indoor unit 29 via a cable.In the indoor unit 29, the signal is down-converted by the oscillation signal from the oscillator 30, and the second IF filter is the surface acoustic wave device of the present invention. ll 31ζ will be sent. The signal that has passed through the second IF filter is transversely waved by a PLL synchronized transverse wave circuit 32 and sent to a video signal processing circuit 33 and an audio signal processing circuit 34, respectively.

FIG. 17 shows the @tear volume frequency characteristic of the 21F filter of the 10th embodiment. The broken line 36 shows the characteristics of the conventional surface acoustic wave device, and the solid line 35 shows the characteristics of the surface acoustic wave device of the present invention. Since the characteristics of the surface acoustic wave device of the present invention faithfully reproduce the signal band, the differential gain characteristic (1) G) and differential phase characteristic (DP) are improved without distorting the signal. Since the characteristic at the band edge became steep, the amount of noise in that part was reduced and the S/N ratio was improved. [Effects of the Invention] As explained above, the present invention allows the step size to be reduced without increasing the step size. In addition, without reducing the aperture length of the T-shaped electrode, a broadband filter with steep shoulder characteristics and improved performance such as side lobe characteristics can be obtained, and the cost of the device can be reduced. It will be done.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of the first embodiment of the present invention, Fig. 2 is an impulse response diagram, Fig. 3 is an attenuation frequency characteristic diagram of the first embodiment, and Fig. 4 is an OJ reflection diagram of the second embodiment. Analysis method explanatory diagram, Figure 5 is a diagram of the second embodiment (/J reduced attenuation station frequency characteristic diagram. Figure 6 is a schematic diagram of the third embodiment, and Figure 7 is an attenuation frequency characteristic diagram of the third embodiment. Fig. 8 is a schematic diagram of CIJ of the fourth embodiment, Fig. 9 is a group delay time frequency characteristic diagram of the fourth embodiment, and Fig. 10 is a diagram of the CIJ of the fourth embodiment.
A schematic diagram of the embodiment, FIG. 11 is a group delay time frequency characteristic diagram of the fifth embodiment, and FIG. 12 is an explanatory diagram of the manufacturing method of the sixth embodiment.
FIG. 13 is an explanatory diagram of the manufacturing method of the seventh embodiment, FIG. 14 is an explanatory diagram of the adjustment method of the communication device of the eighth embodiment, and FIG. 15 is a diagram of the ninth embodiment.
FIG. 16 is a block diagram of the television receiver of the embodiment, FIG. 16 is a block diagram of the dual-layer broadcasting receiver of the tenth embodiment, and FIG. 17 is an attenuation frequency characteristic diagram of the surface acoustic wave filter of the tenth embodiment. . 2, 3.12.15.18...Interdigital electrode...Reflector 13...Basic configuration 20...Inductance 22...Unsatisfactory part 26...Variable inductance 25...Elastic clothing surface arytenoid 31...Surface acoustic wave device cost

Claims (12)

[Claims] 1. Input/output interdigital electrodes are disposed on the surface acoustic wave substrate, and a surface acoustic wave reflector is disposed on at least one side of at least one interdigital electrode to achieve a wide band and frequency characteristics with good shoulder characteristics. A surface acoustic wave device characterized by: 2. Reflectors are arranged on both sides of the interdigital electrode, and the distance between the center of the end electrode of the interdigital electrode and the center of the end electrode of the reflector is determined by setting λ to the surface acoustic wave wavelength n at the center frequency of the filter as a natural number. Both sides are 1/4λ+n/2λ, the reflection coefficient of the reflector is r_a, and the reflection coefficient of the interdigital electrode is r.
2. The surface acoustic wave device according to claim 1, wherein the structures of the reflector and the interdigital electrode are determined so that when _b is ▲a mathematical formula, a chemical formula, a table, etc.▼. 3. The present invention is characterized in that a plurality of pairs of interdigital electrodes and reflectors according to claim 2 are arranged on a surface acoustic wave propagation path, and the interdigital electrodes are electrically connected in parallel. Surface acoustic wave device. 4. When the reflection coefficient of the reflector in the basic configuration according to claim 2 is r_a, and the reflection coefficient of the interdigital electrode is r_b,
The surface acoustic wave device according to claim 5, which satisfies r_b=2r_a. 5. The basic structure according to claim 4 is a reflector comprising a solid type interdigital electrode consisting of two electrode fingers and one electrode finger having the same width as the electrode finger width of each interdigital electrode arranged on both sides of the solid interdigital electrode. 5. The surface acoustic wave device according to claim 4, wherein the surface acoustic wave device is formed by: 6. 2. The surface acoustic wave device according to claim 1, wherein the interdigital interdigital width of the interdigital electrodes on which the reflector is disposed is made asymmetrical in the direction of the surface acoustic wave propagation path. 7. 7. The surface acoustic wave device according to claim 6, wherein the reflector is of interdigital electrode type with a small number of electrode pairs. 8. The reflector disposed in the surface acoustic wave device according to claim 1 is trimmed sequentially from the end to change the reflection coefficient of the reflector or the phase of the reflected wave to obtain desired frequency characteristics. A method for manufacturing a surface acoustic wave device characterized by: 9. A communication device characterized in that the surface acoustic wave device according to claim 1 is used as a filter in its own circuit. 10. The communication device according to claim 9, wherein the surface acoustic wave device according to claim 1 is used as an IF filter between the tuner 1F output of the television receiver and the detection circuit, and the audio carrier level is suppressed and the chroma carrier level is increased. . 11. 2nd I in the indoor unit of the satellite receiver
10. The communication device according to claim 9, wherein the surface acoustic wave device according to claim 1 is used as the F filter. 12. A circuit consisting of a variable inductance element is connected to the interdigital electrode type reflector according to claim 7 used in the surface acoustic wave device of a communication device according to claim 9, and the inductance value of the circuit is sequentially changed. 1. A method for adjusting a communication device, the method comprising changing the reflection coefficient or the phase of a reflected wave of a communication device to obtain desired frequency characteristics.